Mechanistic origins of the high-pressure inhibition of methanol dehydration rates in small-pore acidic zeolites

摘要: Abstract Turnover rates of Bronsted acid-catalyzed methanol dehydration to dimethyl ether become inhibited at high pressures (>10 kPa, 415 K) on small-pore zeolites (CHA, AEI, LTA, LEV), irrespective the distribution framework Al and their attendant H+ sites, but not medium-pore or large-pore zeolites. High-pressure kinetic inhibition occurs concomitantly with stabilization higher-order clusters (e.g., trimers, tetramers) observed experimentally by physisorption liquid-like appearance vibrational modes for in IR spectra, consistent attenuation such higher temperatures (>450 K) that result decreased coverage. DFT-predicted coverage phase diagrams confirm form pressure temperature ranges corresponding onset experimentally, are reactive excess increases apparent barriers kinetically relevant transition states eliminate thus inhibit turnover rates. This combined experimental theoretical investigation provides precise mechanistic interpretation high-pressure acid rigorous analysis enables development models account diverse structures precursors dehydrate ether, methods assess prevalence serve as inhibitory intermediates within during conversion.